The present invention relates to a magnetized pulsar ring used for detection of the rotational frequency, etc. of a rotary body, and a rolling bearing device with a sensor using the magnetized pulsar ring.
In a rolling bearing device that supports a wheel of an automobile, etc., a sensor for detecting the rotation speed of the wheel is built in order to control an anti-lock brake system, etc. Such a conventional rolling bearing device with a sensor has a magnetized pulsar ring set at an inner shaft (rotating ring), and a magnetic sensor that faces the magnetized pulsar ring, as described in the following JP-A-2006-220270, for example. The above magnetized pulsar ring is attached to the rotating ring so as to be integrally rotatable therewith by mixing magnetic powder, such as ferrite, into an elastic member composed of rubber, etc., and by vulcanizing and adhering the elastic member to an axial outside surface of a rotating-ring-side member (slinger) of a sealing device that seals an annular opening between the inner and outer rings. Further, a plurality of N and S poles are alternately arranged in the magnetized pulsar ring in its peripheral direction. Meanwhile, since the magnetic sensor is provided with a magnetism detecting element, its detection surface is arranged axially outside the rotating ring so as to face a detected surface of the magnetized pulsar ring. Also, the magnetic sensor is configured so as to detect a change in magnetic field from the magnetized pulsar ring according to the rotation of the rotating ring, thereby detecting the rotation speed of the rotating ring.
In the rolling bearing device with a sensor in the above conventional example, there is a case that the magnetized pulsar ring is weak in strength because it is formed of a magnetic material using an elastic body, such as rubber, damage or wear is caused in the magnetized surface of the magnetized pulsar ring due to dust or the like penetrated from the outside, and magnetic properties deteriorate.
For this reason, instead of a magnetic material using an elastic body, such as rubber, it is considered that, for example, a plastic magnet having excellent scratch resistance or wear resistance is used. By using the plastic magnet, deterioration of magnetic properties caused by damage or wear can be suppressed.
On the other hand, the plastic magnet is formed by mixing magnetic powder, such as ferrite, and resin, and thus coefficients of thermal expansion differ largely between the plastic magnet, and a metallic member on the side of the rotating ring to which the magnetized pulsar ring is fixed. Further, the plastic magnet has excellent scratch resistance or wear resistance, as compared with the elastic body, such as rubber, whereas it has high brittleness, and is apt to be damaged by deformation.
For this reason, in a case where the magnetized pulsar ring composed of the plastic magnet is adhered or fixedly press-fitted to a member on the side of the rotating ring, a difference is caused in deformation amount between the magnetized pulsar ring and the member on the side of the rotating ring due to a temperature change, etc. Also, if an excessive deformation stress acts on the magnetized pulsar ring, there is a fear that the magnetized pulsar ring may be damaged.
Another related rolling bearing device with a sensor is shown in FIG. 21 (refer to JP-A-2003-279587).
Referring to FIG. 21, the rolling bearing device with a sensor includes a rolling bearing 141, a sensor unit 142 provided in the rolling bearing, and a magnetized pulsar ring 143 that is a portion to be detected.
The rolling bearing 141 includes an outer ring 144 that is a fixed ring, an inner ring 145 that is a rotating ring, and balls 146 that are a plurality of rolling elements arranged between the outer and inner rings.
The magnetized pulsar ring 143 is composed of a supporting member 147 fixed to the inner ring 145 and a magnetized element 148 provided in the supporting member 147.
The sensor unit 142 has a case 149 fixed to the outer ring 144, and a magnetic sensor 150 fitted into the case 149, and faces the magnetized pulsar ring 143 from the axial outside.
The supporting member 147 of the magnetized pulsar ring 143 includes a cylindrical portion 147a fitted to an outer periphery of the inner ring 145, and an outward flange portion 147b provided at a right end of the cylindrical portion 147a, and rotates relative to the magnetic sensor 150 to thereby cause a change in flux density.
As such a magnetized pulsar ring, there is a pulsar ring of a type that is integrated with a sealing unit. As a rolling bearing device with a sensor using the pulsar ring, as shown in FIG. 22, there is known a rolling bearing device (refer to JP-A-2005-098387) including a rolling bearing 151 having a fixed ring 152, a rotating ring 153, and rolling elements 154 arranged between both the rings 152 and 153, a fixed-side sealing member 155 having a core 156 fixedly fitted to the fixed ring 152 and an elastic seal 157 attached to the core 156, a rotation-side sealing member 158 having a cylindrical portion 159 fixedly fitted to the rotary shaft 153 and a flange portion 160 connected to an axial end of the cylindrical portion 159 and extending toward the fixed-side sealing member 155, a sensor 161 supported on the fixed-side sealing member 155 via resin 162, and a magnetized element 163 provided at a side face of the flange portion 160 of the rotation-side sealing member 158. In this rolling bearing device with a sensor, the rotation-side sealing member 158 and the magnetized element 163 correspond to a magnetized pulsar ring, and there is advantage in that the fixed-side sealing member 155 with the sensor 161, and the rotation-side sealing member 158 (magnetized pulsar ring) with the magnetized element 162 can be assembled (packed) in advance.
In the above magnetized pulsar ring, the magnetized element that is formed as magnetic powder that has rubber as a binder may be damaged due to foreign matters.
Thus, it is considered that scratch resistance is increased using a resin bonded magnet as the magnetized element. However, in a case where the resin bonded magnet is used, the magnet is apt to be split because it is relatively weak in thermal shock and fixation of the magnetized element to the supporting member is difficult.